Great, it sounds like this might be easier than I expected. Thanks very
much.
Did you have any thoughts on my diagnosis of the problem (the poor
nonlinear solver convergence being caused by missing Jacobian elements
representing interaction between the sources)?
- Adrian
On 20/05/24 12:41 pm, Matthew Knepley wrote:
On Sun, May 19, 2024 at 8:25 PM Barry Smith <bsm...@petsc.dev> wrote:
You can call MatSetOption(mat,MAT_NEW_NONZERO_LOCATION_ERR) then
insert the new values. If it is just a handful of new insertions
the extra time should be small. Making a copy of the matrix won't
give you a new matrix that is any faster to
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You can call MatSetOption(mat,MAT_NEW_NONZERO_LOCATION_ERR)
then insert the new values. If it is just a handful of new
insertions the extra time should be small.
Making a copy of the matrix won't give you a new matrix that
is any faster to insert into so best to just use the same matrix.
Let me add to Barry's answer. The preallocation infrastructure is now
not strictly necessary. It is possible to just add all your nonzeros
in and assembly, and the performance will be pretty good (uses
hashing etc). So if just adding a few nonzeros does not work, we can
go this route.
Thanks,
Matt
Barry
On May 19, 2024, at 7:44 PM, Adrian Croucher
<a.crouc...@auckland.ac.nz> wrote:
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hi,
I have a Jacobian matrix created using DMCreateMatrix(). What would be
the best way to add extra nonzero entries into it?
I'm guessing that DMCreateMatrix() allocates the storage so the nonzero
structure can't really be easily modified. Would it be a case of
creating a new matrix, copying the nonzero entries from the original one
and then adding the extra ones, before calling MatSetUp() or similar? If
so, how exactly would you copy the nonzero structure from the original
matrix?
Background: the flow problem I'm solving (on a DMPlex with finite volume
method) has complex source terms that depend on the solution (e.g.
pressure), and can also depend on other source terms. A simple example
is when fluid is extracted from one location, with a pressure-dependent
flow rate, and some of it is then reinjected in another location. This
can result in poor nonlinear solver convergence. I think the reason is
that there are effectively missing Jacobian entries in the row for the
reinjection cell, which should have an additional dependence on the
solution in the cell where fluid is extracted.
- Adrian
--
Dr Adrian Croucher
Senior Research Fellow
Department of Engineering Science
Waipapa Taumata Rau / University of Auckland, New Zealand
email:a.crouc...@auckland.ac.nz
tel: +64 (0)9 923 4611
